This research project was planned to define molecular mechanisms and metabolic pathways involved with the process of conversion of very low density lipoproteins (VLDL) and chylomicrons to low density lipoproteins (LDL) and high density lipoproteins (HDL). It has been postulated that the LDL and HDL represent end products of the non-triglyceride constituents of VLDL and chylomicrons which are not metabolized during fat transport. According to this hypothesis, LDL is derived from core-constituents, and HDL from surface constituents of the triglyceride-rich lipoproteins. Both the LDL and HDL therefore are products of lipoprotein lipase mediated triglyceride hydrolysis in VLDL and chylomicrons. The studies carried out during the first project year have established proper methodology and explored several experimental approaches relevant to the goals of the project. In particular, progress was evident in understanding the pathways leading to the conversion of VLDL to LDL. At the end of 10 months of research, we can form LDL-like particles through the activity of several different enzymes from several differet VLDL precursors and can modify those LDL-like particles by simple physiological means. In addition, it has been shown that HDL-like particles are generated from the surface of the lipolyzed lipoproteins. A better understanding of these two processes will hopefully be gained by the end of the study.